1. Field of the Invention
The invention relates to robots. More particularly, the invention relates to robotic alignment of objects (or openings in the objects) that may displace over time.
2. Description of the Prior Art
Processing of substrates is an integral part of producing integrated circuits and is generally known in semiconductor wafer technology. Wafers, which are one form of substrate, are typically five to eight inches in diameter. A single wafer can be exposed to a number of sequential processing steps including, but not limited to, chemical vapor deposition (CVD), physical vapor deposition (PVD), etching, planarization, and ion implantation. Two important goals of all semiconductor processing are to keep the substrates as clean from impurities as possible while enhancing throughput of substrates through many process chambers.
End effectors or robot blades are the portions of the robot that directly supports the substrate. Robots are often used to transfer a substrate from a cassette to an entrance load lock. The same or a different robot(s) is then used to transfer the substrates from that entrance load lock into one or more process chambers, then into an exit load lock. Finally the same or a different robot(s) moves the substrate from the exit load lock into the cassette once again.
The use of robots with end effectors is very desirable in these applications because robots do not contaminate the substrate (if designed properly). Robots can process a large number of substrates through many different processing technologies, and robots can perform repetitive tasks very accurately. Human handling of a substrate, by comparison, lead to contamination of the substrate. As the trend to miniaturize integrated circuits continues (as a result of connections, lines, and vias becoming smaller or thinner), the potential effect of any such impurities becomes more damaging. Thus, the use of robots with end effectors is becoming more essential for transporting substrates in this highly competitive semiconductor field.
Robots with end effectors can also process different substrates from wafers. For example, flat-panel displays formed from non-wafer substrates are getting larger (60 inches and larger). Flat panel displays are capable of providing excellent images and are becoming more accepted, but require a wide and complex variety of substrate processing steps. Considering the electronic complexity and expense of processing flat-panel displays, the benefits of keeping them free from impurities are obvious. A particular difficulty arises when robots are used to transfer large or irregularly shaped substrates or flat-panel displays between load-locks and process chambers. It is difficult to ensure that flat-panel displays align properly with the end effectors of the robots and that once aligned, the substrate can pass through slots or other obstacles in the load locks or process chambers without collisions. A collision may not only chip the flat-panel display, but also create and deposit debris in either the load lock or process chamber. Such debris may result in significant damage to plat-panel displays, including those not directly involved with the collision.
Certain process chambers and load locks operate at high temperatures while others run at much lower temperatures, including room temperature. The temperature variations between the different load locks and process chambers lead to relative thermal expansion or contraction. As a result of thermal expansion, the robot device has difficulty determining the precise position of the load locks and process chambers. Additionally, certain large flat-panel displays can expand thermally by 5 mm during normal processing. Compare this value to the desired substrate transferring accuracy of 1 mm, and the robot may be uncertain of the exact location of the load lock. As the substrate itself undergoes expansion or contraction, the dimensions of overhang of the substrate over the end effector of the robot become variable. It would be desirable to provide a system by which a robot could compensate for the thermal expansion of the substrate.
Another difficulty with the robotic alignment of substrates occurs as a result of carrying the substrate in a cassette. There is typically 10-15 mm of play between the substrates and the cassettes, depending upon the physical configuration of both, i.e. each substrate is not uniformly positioned within its respective cassette. Therefore, even if the robot knows the precise location of the cassette, it may be uncertain of the exact location of the substrate within the cassette. One prior art configuration that attempts to align a substrate within a cassette is known as a xe2x80x9cKachangerxe2x80x9d clamp, which precisely and securely clamps the substrate within a cassette. A disadvantage of this device is that the clamp can abrade the substrate, leading to production of particles. As described previously, particles are highly undesirable in the xe2x80x9ccleanxe2x80x9d environment associated with the production of substrates. Mechanical clamps can also deform with pressure or wear over time such that the substrate would not be precisely located in a perceived position within the cassette.
Therefore, a need exists for a device that can align an end effector of a robot device with a substrate in a processing apparatus.
The invention provides an apparatus and associated method for aligning a substrate using a robotic device. The invention is embodied in a robot device that in alternate embodiments translationally or rotationally aligns an object with a slot. For embodiments providing translational alignment, the robot device comprises a position sensor positioned adjacent to the slot. The translational position sensor determines the position of the object by moving the object relative to the slot until it actuates the position sensor. For embodiments providing for rotational alignment, two position sensors are provided that determine the relative angle between the object and a portion of the robot device and the object.